rondelli



y T. RONDELLI ELECTRIC FURNACE lFiled June 22 1920 3 Sheets-,Sheet l Jan. 15, 1924.

T. RONDELLI ELECTRIC FURNACE 3 Sheets-Sheet 2 Filed June 22l 1920 y. f all??? 1 my f .4.

Jan. 15, 1924. 1,481,223

T. RONDELLI ELEcTnIc Funngcn Filed June 22 1920 a sheets-sheet /J Y e O f6 o o C 6j 19 3/ fzsY 21X 1f f@ Ven/far.

Patented Jan. 15, 1924.

UNITE-D STATES PATENT OFFICE.

TITO 'RONDELLL DE LONDON, ENGLAND.

ELECTRIC FUBNACE.

Application iledilunn:I 22, 1920. Serial No. 399,976.

ondon, Englan haveinvented certainnew .i andusef-ul Improvements in Electric Furnaces (for which I have filed applications as4 follows: Italy, filed,v April 30 1917, No. 159,684; France, filed Mar. l2, 19,19, No. 497,220; andGreabBritain, A ug.f1 0, A19.18, No. 127,458), .of which the folloyving is' a specification.

ljllislinven furnaces and has for its'objectfirnpr'overnnts in electric furnaces of the lindvinfiqhichthe resistant body provides th` ,furnace charriber orcrncible.: i

The object of thisinventionis an arrangement. by ngeans. ofV which. theheat is properly distributed' inthe furnace chamber and the heatl dissipationis reduced.

1.109 el' .biie'cfe'f .he'werent.waarna-? to prevent; tie corrosion fof, the resistant body.

4The irnproyements ,accordingl to vthis in vention result in. an, linoifeasfe theeiiiciency 0f .the furnace @da 'a Cheap manta of the same.

VI n zthe hnprvn resistance` furnaces .coi'nprisins a minr'esaa body 'farmed dat im.- intrupted i Sal@ badn- 'Sayl "a lubla 01'. chamber. of carbon. or graphite, the arts feeding the current are connected direct y to said 'bodyandf heatv is developed to an equal extent throughout the 'several portions4 of said bodyf Therefore'said feeding parts are intensely. heatedby the heat 'transmitted from said bodyand axsfthey4 require l'tobe provided with cooling means for :preventing their .expansion from giving frise :to imperfect contacts and to overheating, thejlarge amountl of heat absorbed by. the feeding parts is dissipated by saidcooling means.

According to this invention afurnace ofthe describedtype the current is 4fed to one or both ends of, said resistant/body by means of a part of low resistance proi-'idinga .large surface of contact with thefrcsistant body and ,havingA a recess filled with refractory material. According to another feature .of this invention a layer, of high resistance material located between the, facing surfaces of the main-resistant body andthe current feeding part. As a large amount of heat is.l deve1- oped in, said layer by Joule effect, the portionl relateS electric resistance.

tions of the furnace adjacent to said layer. are intensely heated and by the provision of said layer in Contact with the bottom of the furnace chamber or Crucible a very in! tense heating is obtained at said bottom as. required for carrying out metallurgical treatments.

Onfthe contrary in known resistance furn'acest'he resistance and hence the heatin are low in the zone occupied by thern'eta because the current tends to flow through this rnetal.

VFurther by inserting the resistant layer above referred to between the furnace'chamber or. Crucible and the current feeding part the voltage drop across the furnace poles maybe made as high as desired even when the resistance of the main bodyis comparatvely low. Thus the current intensity does not need to have an exceedingly high value for obtaining la desired heating effect.

On the annexed drawings are' shown some embodimentsofi this invention. i

In said ldrawings'ligure 1 is a central vertical; section of a crucible furnace according toI :this invention; FigureQ is a similar section of at ,Inodifiedconstruction'g Figure 3 isa central section of a furnace comprising two erucibles which provide the furnace chamber; Figure 1 is a central verticai'section of anoth'erconstructiong Figure is a side vieiv'offthis construction and Figure G is a horizontal section on rtheline G-f-G, A Figures4 and 5. I

The furnace shown by Figure 1v comprises a casing. 8 of refractory material which is provided at its bottom lwith ablolr 5 of rtefractory material and a hollow conducting ring 4 adapted to beconnected withone of the feeding conductors, not shown.. On'sai block is located a member 2 ofcomparatire- 1y large size which contacts with said ring 4 and is provided with areccss in its portion opposite the block 5; this recess is filled with a.` layerof reducing material 6, say amorphous graphite, powder. 0n the topl` lof the 1 einher 2 `is located a layer 3 ofa rnaterial aijing ,a Vhigher, ,electrical resistance than said member 2, as graphite of lainellar structure. i The crucible 1 is inadeof carbon, graphite orfother suitable Vniaterizafl andll'iears on said layer .3; at its upper mouth this crucible isencircled byY a current feeding ring 4. The mouth of the Crucible closed by a plug 0f refractory. material and .the tra@ between the casing 8 and the Crucible l is filled with a proper material 9 such amorphous graphite in powdered condition. irhch is a material having practically no conductivity. l The Construction shown by Figure :2 is similar to that above described in all respects, excepting that the member 2 has a much larger diameter as comparedv-ith the diameter of the region of the cruciblc contactin with the intermediate layer 3.

In igure 3 is shown a furnace comprising a chamber provided by two. crilcibles 1-1' arranged with their axes horizontal and their mouths close to each other; the end of each crucible bears a-gainst a member 2 with an interposed layer 3 of resistant `material and the current is supplied'by4 conducting rings each embracing one of saidnmemf bers 2. described in connection with other figures the crucibles 1 1 ar'e` enclosed within a refractory casing 3 and a lil-ling of nonconducting material 9J In the furnace built Aas aboneA described the current flowing'from one to thefother of the rings 4 passes through' themember or members 2 layer-'or layers 3 and the' -.body of the Crucible, and the highest development of heat is obtained in 'each'flayer B O'Wing to the highA resistance ofthe material formincthis layer. ,i

herefere the-Crucible is. heated by am heat developed Joule effect in its own wall andfurther itis portion contacting with theV layer 3 ishifohly heated byftheheat developed in said ayer; the temperature of the crucible thus decreasing Vfrom itsbottom towards its mouth. y A On the contrary the heating by J oulee'ect is ne ligiblelgin the member 24 on account of the size offthismemberl The feeding parts 4 andthe conductors connect/ed thereto are prevented from absorbing a large amount of heat on account 'of their distance from the hottest parts of the furnace and on account of the block 5 and pluf 7 intercepting any line of radiation fromliot portions of the furnace. i

'The layer 9 of amorphous graphite forms a reducinor medium encircling theresistant body 1 and thus this body is prevented from being burnt and giving rise to any reaction with the refractory material of the casing. The layer 3 may conveniently consist of lamellar graphite and'thusit may be easily re lacediata very lowfcost.

y the constructlo'n' according to this inventionthe life of theessential parts of the 'furnaceis extended andthe cost of its operation 'and maintenance is reduced. p

The arrangement of a layer 3 of the described 'character between the' member 2 connected with the current feeding parts and the crucible provides also the advantage that the furnace may -be caused to`worlr with any desired voltage drop across its poles, he cause by modifying the thickness or the nature of the layer 3 any desired value may be imparted to the resista-nce of the furnace notwithstanding the Crucible has a low resistance as usual; said layer 3 may he easily replaced when the furnace is not in operation.

Preferably the filling 9 consists of powdered amorphous graphite which has practically no conductivity; the portion of this l'illin which contacts with the outer surface o the crucible undergoes a partial modification and hardens under the high temperature to which it is subjected, Whereby it takes up a conductivity which compensates for possible corrosions of the inner surface of the crucble.

Figures 4, 5.and 6 show a further embodiment of the furnace according to this invention. In this construction the crucible 1 is enclosed Withi'na. refractory sleeve 8 mount ed in a metal casing 10; this casing is pro- .vided with trunnions lljournalled on stand ards 12. The bottom of the casing 10 is closed by a plu 5 of refractory material and carries the fee ing ring 4'; the crucible 1 is supported by a hollovi1 member 2 which bears on the plufg 5 through the intermediary of a layer 6 o reducing material and between the bottom of 'the crucible 1 and the member 2 is locateda "layer 3 of high resistance material as lamellar graphite.

Said member 2 may conveniently consist of the bottom of a Crucible out of service and the layer 6 may consist of amorphous graphite.

The outer portion of the mouth of the crucible is encircled by a conducting ring 4- intended to feed the current to the furnace in cooperationwiththe bottom rinor 4.

Each of said feeding rings consists of'two semi-circular segments which are con nected to the ends 'of resilient blades 13-"13'. Thefirst blade 13 is connected by means of insulated blocks 18 to the conductor 19 (Figure 5) 'and is thereby connected to one terminal of the source of the current suppl the other blade 13 is connected through t e insulating block 18', to the conductor 19 and tov the opposite pole of said source.

As shown on the drawing the sevments forming said rings 4-4' are made lhollow and to provide for a Water circulation; this water is fed thro-ugh ducts 14 located in the trunnions 11.

The mouthof thecrucible 1 is closed by a plu@ 7 of refractory material which is secure to a cover plate 7'; this plate Tf lis held in position by hand operated nuts 15 each of which engages a screw-threaded rod 16 connected -to the casing 10 through the intermediary 'of 'a spring'18 and a sleeve 19.

As shown by Figure 6 the segments forming each ring '4 -4 are clamped together and orced on the cooperating portion of the crucible 1 cr member 2 by means of bolts 17.

The space between the refractor sleeve 8 and the Crucible 1 is lilled with a ayer 9 of amorphous graphite in powdered condition, as described in connection with other fiffures.

What I claim as my invention and ldesire to ,secure by United States Letters Patent l. In an electric resistance furnace comprising a main resistant body providing the furnace-chamber or crucible; a member of large size made of a material of the same character as said main resistant body for feeding the current to said body, said member being provided with a recess on its side opposed to its face adjacent to said main resistant body, refractory material located in said recess, a layer of high resistance material located between said member and the facing portion of said main resistant body and conductors contacting Wth the peripheral surface of said member and connected with a pole of a current supply.

2. In an electric resistance furnace comprising a crucible of resistant material provided with means connecting its mouth end With a pole of a current supply; a member of large size and made of a material of the same character as said Crucible, this member being located adjacent to the bottom of said cruclble and being recessed on its side opposed to its face adjacent to the crucible, refractory material located vin said recess, a layer of high resistance material located between said member and crucible and means contacting with the peripheral surface of said member for connection with the other pole of said current supply.

Si ned at London, England, this 28th day of ay, A. D. 1920.

TITO RONDELILI. 

